Heat exchanger with plate structure

ABSTRACT

The invention relates to a heat exchanger ( 1 ) with plate structure, comprising a stack ( 6 ) of plates composed of circular heat transfer plates ( 10 ) by welding and fitted inside a housing unit ( 2 ) used as a pressure vessel, whose periphery is provided with flow guides ( 21, 22 ), by means of which the second heat transfer medium is guided to desired ducts in the stack ( 6 ) of plates. By means of spacing plates ( 32 ) fixed inside the flow guides ( 21, 22 ), it is possible to arranged several draughts for the stream of the heat transfer medium.

[0001] The invention relates to a welded heat exchanger with a platestructure for heat transfer between substances in the same state or indifferent states, such as a gas or a liquid. The heat transfer surfacesconsist of heat transfer plates attached to each other and collected ina stack of plates which are circular in shape and which have at leasttwo flow openings for the supply and discharge of a heat transfer mediumthrough ducts formed by the plates. The plates of the heat exchanger arewelded together in pairs at the peripheries of the flow openings, andthe plate pairs are connected to each other by welding the plates of theplate pairs at their peripheries to the plates of other plate pairs. Thestack of plates is fitted inside a cylindrical housing unit used as apressure vessel. The invention relates to an arrangement, by means ofwhich it is possible to lead the stream of the second heat transfermedium through the housing unit into and from desired ducts in the stackof plates in a desired direction.

[0002] A conventional plate heat exchanger is composed of superimposedplates which form a stack of plates which is clamped between two endplates by means of tie bars. The ducts formed by the plates and the flowopenings connected thereto are sealed at their peripheries by means ofseparate sealings. The plates of such plate heat exchangers aretypically rectangular in shape, and the flow openings, usually four innumber, are placed in the vicinity of the corners. In conventional plateheat exchangers, the streams of the heat transfer medium are normallyarranged in such a way that the flow openings at opposite corners areused as inlet and outlet ducts, wherein the streams of the primary andsecondary sides flow in adjacent ducts formed by the heat transferplates. In conventional plate heat exchangers, it has been possible tostep the streams of the primary and secondary sides and to divide theminto several draughts by closing the flow openings at desired locations.

[0003] Conventional tubular heat exchangers, in which the second heattransfer medium streams in a bundle of tubes fitted inside a cylinder,normally apply plate-like flow guides which are perpendicular to thebundle of tubes. Thus, the stream of the heat transfer medium inside thecylinder, which normally flows to the secondary side, will pass severaltimes through the bundle of tubes. The number of flow guides can be usedto accelerate the stream inside the cylinder and to induce turbulence inthe stream, wherein the heat transfer properties can be improved.However, the dimensioning of tubular heat exchangers is normally basedon the heat transfer inside the tubes, which is normally smaller thanthe heat transfer outside the bundle of tubes. The large size of tubularheat exchangers is largely due to poor heat transfer inside the tube.The diameter of the cylinder of the tubular heat exchanger is normallysmall in relation to the length of the cylinder. The stream inside thecylinder is, in most cases, arranged to flow from one end to another.Because of the shape of the heat exchanger, there are normally nosealing requirements set for the flow guides used as the support meansfor the bundle of tubes.

[0004] In heat exchangers composed of circular heat transfer plates, inwhich the stack of plates is placed inside a cylinder, it has beenproblematic to arrange the stream of the secondary side inside thecylinder in such a way that there is no by-pass flow. In heat exchangerstructures of this kind, the stream passing through the flow guidespasses almost all the heat transfer surfaces, thereby substantiallyreducing the heat transfer properties. For this reason, flexible flowguides made of a metal sheet have been used in heat exchangers, to pressrubber sealings or the like towards the outer surface of the stack ofplates and towards the inner surface of the housing of the heatexchanger. The function of these flow guides is to prevent thetransverse by-pass flow between the stack of plates and the housing.Thanks to their flexible structure, these flow guides have served wellin operation. On the contrary, the stiff spacing plates which have beenused to divide the stream on the secondary side into several draughtshave often proved to be leaky, even though they have been provided withrubber sealings against the stack of plates and the housing.

[0005] The aim of the present invention is to provide a welded heatexchanger made of circular heat transfer plates, which has the goodpressure resistance properties of the tubular heat exchanger and whoseheat transfer properties correspond to those of a conventional plateheat exchanger and whose modification possibilities to provide severaldraughts on the primary and secondary sides correspond to the propertiesof a conventional plate heat exchanger.

[0006] The invention is based on the idea that flow guides with aninternal tube structure are provided outside the stack of plates, insidethe housing of the heat exchanger, which flow guides are fixed at leastpartly to the stack of plates but, through a small hole or openingtherein a connection is formed to the closed space between the housingand the stack of plates, whereby the stream through the space isprevented and the flow guides can be dimensioned as parts not belongingto the pressure vessel.

[0007] More precisely, the heat exchanger with plate structure accordingto the invention is characterized in what will be presented in thecharacterizing part of claim 1.

[0008] In the heat exchanger with plate structure according to theinvention, flow guides for guiding the secondary heat transfer mediumwith an internal tube structure, fixed to the stack of plates, areprovided on the periphery of the stack of plates; there are at least twoflow guides, and they are placed on opposite sides of the stack ofplates to guide the stream into and from desired ducts of the stack ofplates. To divide the secondary stream into several draughts, spacingplates are mounted inside the housing of the flow guides, the platestack side of the spacing plates being sealed with a rubber sealing orthe like. The flow guides are connected to the inlet and outlet passagesof the housing of the heat exchanger with plate structure by means oftubes which are located partly inside them and of which at least one iswelded to the inner surface of the passage. In the heat exchangeraccording to the invention, the heat transfer medium has free access,through a hole in the flow guide or through a tube not connected to thepassage, to the space between the stack of plates and the housing, inwhich the heat transfer medium cannot, however, flow anywhere, the spacebeing closed in other parts.

[0009] Significant advantages are achieved by the heat exchanger withplate structure according to the invention. The streams on the primaryand secondary sides can be divided in a desired manner, whereby thenumber of draughts can be freely selected, depending on the propertiesof the heat transfer media and the stream quantities. The heat exchangerwith plate structure can be used as a concurrent, countercurrent orcross flow heat exchanger. In the heat exchanger with plate structureaccording to the invention, the heat transfer properties of the heatexchanger are not reduced by by-pass flows. The flow guides are plateparts with a light-weight structure, because they are not parts of thepressure vessel.

[0010] In the following, the heat exchanger with plate structureaccording to the invention will be described in more detail withreference to the appended drawings, in which

[0011]FIG. 1 shows schematically the heat exchanger with plate structureaccording to the invention in a side view,

[0012]FIG. 2 shows schematically the heat exchanger with plate structureas shown in FIG. 1 in a cross-section,

[0013]FIG. 3 shows schematically the cross-section of the heat exchangerwith plate structure as shown in FIG. 1, at the location of line A-A,

[0014]FIG. 4 shows schematically the outlet passage of the housing ofthe heat exchanger with plate structure according to the invention, in across-section, and

[0015]FIG. 5 shows schematically the inlet passage of the housing of theheat exchanger with plate structure according to the invention, in across-section.

[0016] In the following, the invention will be described in more detailwith reference to the appended drawings. FIGS. 1 to 5 show an embodimentof the heat exchanger with plate structure 1 according to the invention,with two draughts both on the primary side and on the secondary side.The housing unit 2 used as a pressure vessel for the heat exchanger withplate structure comprises a housing 3 and end plates 4 and 5 which arefixed to the housing 3 in a stationary manner. The housing unit 2accommodates a stack 6 of plates forming the heat transfer surfaces,which stack can be removed for cleaning and maintenance, for example, byconnecting one of the ends 4, 5 with a flange joint to the housing 3. Aheat transfer medium flowing inside the stack 6 of plates forms aprimary stream which is led to the stack 6 of plates through the endplate 5 via an inlet passage 7 and is discharged via an outlet passage 8in the opposite end 4. The passage of the primary stream is illustratedwith arrows 9.

[0017] The stack 6 of plates forms the heat exchange surfaces of theheat exchanger 1, which are composed of circular grooved heat transferplates 10 connected to each other. The heat transfer plates 10 areconnected together in pairs by welding at the peripheries of flowopenings 11 and 12, and the pairs of plates are connected to each otherby welding at the peripheries 13 of the heat transfer plates 10. Theflow openings 11 and 12 constitute the inlet and outlet passages of theprimary stream inside the stack 6 of plates, through which passages theheat transfer medium is led and discharged from the ducts formed by theheat transfer plates. By closing the flow openings 11, 12, the stream onthe primary side can be divided into several draughts. FIG. 2 shows thatclosing the flow passage 11 at point 14 changes the stream of theprimary side into two draughts.

[0018] The stack 6 of plates is assembled and pre-tightened by weldingthe end plates 15, 16 in the stack 6 of plates together with sidesupport plates 17, 18. To avoid a by-pass flow of the heat transfermedium in the space between the stack 6 of plates and the side supportplates 17, 18, the space is provided with rubber sealings 19, 20 or thelike before the assembly. The housings 23, 24 of the flow guides 21, 22are connected at their sides by welding to the side support plates 17,18. The ends of the flow guides 21, 22 are closed with separate endplates 25, 26, or by welding the housings 23, 24 of the flow guides 21,22 directly to the end plates 15, 16 of the stack 6 of plates.

[0019] The heat transfer medium of the stream on the secondary side isled into the housing unit 2 through an inlet passage 27 penetrating thehousing 3 and is discharged via an outlet passage 28. The stream on thesecondary side is illustrated with arrows 29 in FIG. 2. The flow guide22 is connected to the inlet passage 27 and the outlet passage 28 bymeans of tubes 30 and 31 which are partly fitted in the inlet and outletpassages. The flow guide 22 is divided into two parts by means of aspacing plate 32 welded in the housing 24 of the flow guide 22. A rubbersealing 33 or a corresponding arrangement is used between the spacingplate 32 and the stack 6 of plates to prevent a by-pass flow in the flowguide 22. The number of draughts on the secondary side can be increasedby adding spacing plates 32 in the flow guides 21, 22. FIGS. 4 and 5show how the tubes 30, 31 related to the flow guide 22 are partly fittedinside the inlet and outlet passages 27 and 28. In the embodiment of theinvention shown in FIGS. 1 to 5, the tube 30 fitted inside the inletpassage 27 is tightly welded with a seam 34 to the inner surface of theinlet passage 27. Between the outlet passage 28 and the tube 31 fittedtherein, however, a gap is left, through which the heat transfer mediumis allowed to flow into the space 35 between the housing 3, the flowguides 21, 22 and the support plates 17, 18 for the stack 6 of plates.

[0020] The heat exchanger 1 with plate structure according to theinvention is normally used by controlling the streams on the primary andsecondary sides. The only limitation to the use of the device is thefirst starting up, wherein it must be taken into account that the flowguides 21, 22 are not parts of the pressure vessel and that a certaindelay time must be reserved for the space 35 to be filled up with theheat transfer medium. It is obvious for anyone skilled in the art thatonly one embodiment of the inventive idea has been presented above,which may naturally vary within the scope of the claims. For example,the number of draughts on the primary and secondary sides of the heatexchanger 1 may be different, and the locations of the inlet and outletpassages 7, 8, 27, 28 can be almost freely selected. The connection ofthe flow guides 21, 22 to the inlet and outlet passages 27, 28 of thesecondary side can be arranged in such a way that the stack 6 of platescan be easily detached from the housing unit 2. Also, the filling up ofthe space 35 inside the housing 3 with the heat transfer medium can beimplemented in a way different from that presented above.

1. Heat exchanger (1) with plate structure, preferably welded, intendedfor the heat transfer between substances in the same or in differentstates, such as a gas and a liquid, comprising a closed stack (6) ofplates consisting of circular heat transfer plates (10) used as heattransfer surfaces and connected to each other at their peripheries (13)or at the peripheries of their flow openings (11, 12), one heat transfermedium flowing inside said stack (6), a housing unit (2) used as apressure vessel and consisting of ends (4, 5) supporting the stack (6)of plates and the surrounding housing (3), another heat transfer mediumflowing inside said housing unit (2), and inlet and outlet passages (7,8, 27, 28) for the heat transfer media flowing in the stack (6) ofplates and in the housing unit (2), extending through the housing (3)and the ends (4, 5), characterized in that on the periphery (13) of thestack (6) of plates, inside the housing (3), there are flow guides (21,22) for the heat transfer medium flowing inside the housing unit (2),having an internal tube structure and being at least partly connected tothe stack (6) of plates, that there are at least two flow guides (21,22) with an internal tube structure, being preferably arranged onopposite sides of the stack (6) of plates, and that the flow guides (21,22) are connected to the inlet and outlet passages (27, 28) of thehousing unit (2) by means of tubes (30, 31) arranged at least partly inthe passages, of which at least one is connected in a leakproof manner,preferably by welding, to the inner surface of the inlet and/or outletpassage (27, 28) of the housing unit (2).
 2. Heat exchanger (1) withplate structure according to claim 1, characterized in that the flowguides (21, 22) are connected at their sides to the side support plates(17, 18) of the stack (6) of plates and at their ends to separate endplates (25, 26) or to the end plates (15, 16) of the stack (6) ofplates.
 3. Heat exchanger (1) with plate structure according to claim 1,characterized in that the flow guides (21, 22) are elements with platestructure which do not belong to the pressure vessel.
 4. Heat exchanger(1) with plate structure according to any of the claims 1 to 3,characterized in that rubber or corresponding sealings (19, 20) arefitted underneath the side support plates (17, 18) for the stack (6) ofplates to prevent a stream between the stack (6) of plates and the sidesupport plates (17, 18).
 5. Heat exchanger (1) with plate structureaccording to any of the claims 1 to 4, characterized in that the spacingplates (32) of the flow guides (21, 22) are preferably connected bywelding to the housings (23, 24) of the flow guides (21, 22), and thatthe edge of the spacing plates (32) on the side of the stack of platesis sealed with a rubber sealing (33) or the like.
 6. The heat exchanger(1) with plate structure according to any of the claims 1 to 5,characterized in that the space (35) between the stack (6) of plates,the flow guides (21, 22) and the housing (3) of the housing unit (2) isfilled with a non-flowing heat transfer medium.
 7. Heat exchanger (1)with plate structure according to any of the claims 1 to 6,characterized in that the flow guides (21, 22) comprise at least oneopening to lead heat transfer medium to the space between the housingunit (2), the stack (6) of plates and the flow guides (21,22).
 8. Heatexchanger (1) with plate structure according to claim 7, characterizedin that said opening is arranged in such a way that the tube (31; 32)fitted inside the inlet or outlet passage (27; 28) is connected to saidpassage (27; 28) in a leaking manner.